The invention relates to polyester laminating compositions useful in the production of polyester resin laminates with improved interlaminar adhesion and a method of preparing same. More particularly, the invention relates to wax-containing polyester laminating compositions which include as adhesion promoters a polyvinyl acetate component or a polyvinyl acetate component in combination with at least one salt of a long chain polyaminoamide and a high molecular weight ester.
Polyester resins have been used for various purposes including the production of laminated articles. In the manufacture of such laminated articles a plurality of layers of polyester resin compositions are successively superimposed. Usually the article is reinforced by incorporating a reinforcing filler such as glass fiber or the like. Typically, the filler may be applied seprately as a mat or fabric which is impregnated with the liquid polyester resin composition or it may be dispersed as short strands in the composition.
In the manufacture of fiber-reinforced polyester resin laminates it is important that the adhesion between superimposed layers is adequate. Good interlaminar adhesion is often difficult to obtain with wax-containing polyester laminating systems, i.e. polyester laminating compositions which include a waxy substance for the purpose of decreasing the evaporation of volatile cross-linking compounds in the compositions, since such waxy substances tend to interfere with the interlaminar properties of these systems.
The unsaturated, polymerizable polyesters which are generally used in the production of such laminates are substantially condensation products of dicarboxylic acids and diols. Generally the dicarboxylic acid component consists primarily of an unsaturated acid and/or anhydride like maleic acid or fumaric acid. A portion of the unsaturated acid or anhydride may be substituted with a saturated acid and/or anhydride such as orthophthalic acid, isophthalic acid, adipic acid or the like. The diol component is normally selected from diols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol and mixtures thereof.
In addition to the polyester component, polyester resin compositions contain volatile reactive monomeric material which is copolymerizable with the unsaturated polyester and which also acts as a solvent for the unsaturated polyester improving the workability of the composition, in particular, the viscosity. Examples of suitable volatile monomeric materials include styrene, vinyl toluene, alpha-methyl styrene, methacrylic acid and methyl methacrylate.
The cure of unsaturated polyester resin laminating compositions is commonly catalysed by free radical catalysts such as suitable peroxides. The cure can be accelerated by further inclusion of cure promoters.
During application of the polyester resin composition and before completion of the polymerization a portion of the volatile monomer, which in most cases is styrene monomer, evaporates. This may lead to insufficient cross-linking at the surface of the resin resulting in an undercured tacky surface. Moreover, evaporation of substances such as styrene is environmentally undesirable. To decrease the evaporation waxy substances such as paraffin wax, montan wax, carnauba wax and the like are usually added to the polyester resin composition. However, even though generally only small amounts of wax are required to reduce the evaporation of volatile monomer materials, the incorporation of wax tends to interfere with the interlaminar adhesion between layers in the cured laminated articles formed from such wax-containing compositions.
Several ways of overcoming this drawback have been proposed but have not always been completely satisfactory. Thus it has been suggested to improve interlaminar adhesion by incorporating into the polyester resin composition compounds such as maleic acid derivatives (U.S. Pat. No. 4,336,169 issued June 22, 1982), unsaturated vinyl compounds (U.S Pat. No. 4,285,845 issued Aug. 25, 1981), an alkylaromatic compound or mono-alcohol (U.S. Pat. No. 4,347,170 issued Aug. 31, 1982), tertiary monoamine (U.S. Pat. No. 4,296,009 issued Oct. 20, 1981), etc.